For those of you who use calibre, is there a way to convert the Amazon kindle books to epub or pdf?

You would have to strip the DRM first. There's some information at the bottom here, including a link on the legal implications: http://dearauthor.com/wordpress/2010/12/05/tips-reading-adobe-epub-and-pdf-books/?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+dearauthor+%28Dear+Author%3A+Romance+Novel+Reviews%2C+Industry+News%2C+and+Commentary%29

I'm not entirely sure it would work then, but they do have mobipocket listed as a format that can be changed "from" or "to."

Thanks Willa.  I didn't really think there was a way, just checking.

I was going to try that but I can't download a Kindle book (even a free one) without installing Kindle for PC on my computer and I really don't want to do that.  I have stripped the DRM from EPUB books before.

You can do it.  I had to download the books to my Kindle for PC, and add a plug-in to remove the DRM.  You add the books to your calibre library & then convert them.   Once you add that plug-in to Calibre, you just convert the Kindle file to whatever format you want.  I don't have my Nook yet, so I haven't actually transferred the pdf files to it to see how they look there, but I opened them on my computer and they were fine.

I'm glad because about half of the ebooks I have are Kindle for PC and I wanted to be able to read them on my Nook!

Sherri, if you want to try it, I can give you the link to the info I found about the plug-in.